"Pickup-day" screens

[wvengen]

In the foodcoop-adam fork, there are screens for actions on the pickup day: (1) receive, (2) distribute, (3) checkout. This is for orders that are finished but not closed.

To get an idea, here are some screenshots.

I'd love to bring these screens to the main Foodsoft code here. This might take a while. This ticket is to keep the overview, other tickets are for specific issues:

• Introduce the notion of a "pickup day", a context where all orders are part of.
• Allow to enter both in unit (e.g. 100g) and in "base unit" (g)
• Add receive screen.
• Add product distribution screen.
• Add ordergroup 'checkout' screen
• Modify ordergroup 'checkout' screen
  This list is not complete, probably, neither necessarily in order.

[wvengen]

p.s. this is currently all in a separate current_orders plugin, which might just work on this version of Foodsoft too. Perhaps.

[wvengen]

This will beimplemented in in #373, except the ability to enter in both unit and "base unit".